Surface treatment refers here to a layering process where a surface layer of a substrate is modified by allowing particles to diffuse in the substrate matrix, or where particles are deposited on the surface such that a surface layer is produced on the substrate. Particles used for this kind of surface treatment are typically very small, the mean particle diameter ranging from 10 to 100 nm. Particles of this size are typically generated in a particle synthesis process where precursor chemicals are exposed to a thermal reactor. In the intense heat of the thermal reactor they undergo specific thermochemical and -physical reactions that lead to development of desired particles.
In industrial applications, the particle synthesis process typically incorporates a source element that applies a nozzle for ejecting a combination of precursor substances for surface treatment particles, and a thermal reactor for transforming the combination of precursor substances to a directed particle flow. Typically the thermal reactor is a turbulent hydrogen-oxygen flame into which the nozzle outlet channels from one or more nozzles eject a spray of materials, either mixed together or through separate outlets.
The problem with surface treatment devices is that temperatures necessary to allow efficient deposition of particles are very high, and heat from a flame achieving these temperatures causes an extreme strain to nozzle materials. Under the intense heat of a flame nozzles tend to deteriorate, as a result of which the quality of the emitted particle flow quickly degrades.